Venting unit for a Die Casting device

ABSTRACT

The invention relates to a venting unit for a die casting device which has a mold cavity that is adapted to be filled with liquid casting material and a gas suction device that is connected to the mold cavity for extracting gas from the mold cavity by suction, the venting unit comprising a flow labyrinth, the inlet of which is adapted to be connected to the mold cavity and the outlet of which is adapted to be connected to the gas suction device. In order to develop the venting unit in such a way that it makes improved evacuation of the mold cavity possible without the risk that liquid casting material can escape from the venting unit, it is proposed according to the invention that the flow cross-section of the flow labyrinth is variable. Furthermore, a die casting device with a venting unit of this kind is proposed.

This application is a continuation of international application number PCT/EP2008/006180 filed on Jul. 26, 2008 and claims the benefit of German patent application no. 10 2007 054 520.9 filed on Nov. 6, 2007.

The present disclosure relates to the subject matter disclosed in international application number PCT/EP2008/006180 of Jul. 26, 2008 and German application number 10 2007 054 520.9 of Nov. 6, 2007, which are incorporated herein by reference in their entirety and for all purposes.

BACKGROUND OF THE INVENTION

The invention relates to a venting unit for a die casting device which has a mold cavity that is adapted to be filled with liquid casting material and a gas suction device that is connected to the mold cavity for extracting gas from the mold cavity by suction, the venting unit comprising a flow labyrinth, the inlet of which is adapted to be connected to the mold cavity and the outlet of which is adapted to be connected to the gas suction device.

The invention also relates to a die casting device with a venting unit of this kind.

Die casting devices are known, for example, from DE 20 2005 019288 U1. They have a mold cavity, into which liquid casting material, for example molten aluminum or magnesium, can be injected. To avoid air bubbles being trapped in the casting material, which is at first liquid and then hardens in a very short time, with the trapped air bubbles possibly impairing the quality of the casting produced, the air can be extracted from the mold cavity by means of a gas suction device. The extraction of air from the mold cavity may take place before and during the filling of the mold cavity. To avoid liquid casting material being able to escape from the mold cavity and reach the gas suction device or a venting valve disposed upstream of it, disposed between the mold cavity and the gas suction device is a venting unit which forms a flow labyrinth, the inlet of which is adapted to be connected to the mold cavity and the outlet of which is adapted to be connected to the gas suction device. The inlet may, for example, be connected to the mold cavity by way of a venting channel, and the outlet of the flow labyrinth may be connected to the gas suction device by way of a suction line. The flow labyrinth can be used for extracting gas from the mold cavity. If liquid casting material enters the flow labyrinth, it solidifies within the flow labyrinth, so that the flow connection between the mold cavity and the gas suction device is interrupted. Venting units of this kind, which can be used for extracting gas from the mold cavity and in the flow labyrinth of which entering casting material solidifies, are also referred to as chill block systems or washboards.

The main task of the gas suction device of a die casting device is to evacuate a certain amount of air from the mold cavity within a short time, i.e. within a few seconds. The air is in this case sucked out of the mold cavity through relatively narrow gaps. The narrow gaps impair the extraction capability. In many cases it has been found that, even though powerful gas suction devices are provided, the mold cavities are only evacuated unsatisfactorily.

It is an object of the present invention to develop a venting unit of the type mentioned at the beginning in such a way that it makes improved evacuation of the mold cavity possible without the risk that liquid casting material can escape from the venting unit.

SUMMARY OF THE INVENTION

This object is achieved according to the invention in the case of a venting unit of the type mentioned at the beginning by the flow cross-section of the flow labyrinth being variable. This provides the possibility of reducing flow losses within the flow labyrinth when gas is extracted from the mold cavity, since a relatively large flow cross-section can be chosen for the flow labyrinth for the extraction of gas from the mold cavity. The evacuation of the mold cavity can be significantly improved as a result. However, to be able to avoid liquid casting material being able to flow through the flow labyrinth and escape from the venting unit, the flow cross-section of the flow labyrinth can be reduced, so that it is ensured that inflowing casting material reliably solidifies within the flow labyrinth.

It is of advantage if the flow cross-section of the flow labyrinth is adapted to be varied by liquid casting material flowing into the flow labyrinth. This provides the possibility of choosing the flow cross-section to be comparatively large at the beginning of the casting operation, in order to be able to extract gas effectively from the mold cavity. The extracting operation may continue until casting material filled into the mold cavity enters the flow labyrinth. The inflowing casting material can then bring about the reduction in the flow cross-section of the flow labyrinth, for example by the inflowing casting material impinging with great force on a portion of the wall of the flow labyrinth. The impingement of the portion of the wall with the surge of inflowing casting material can then be used for reducing the flow cross-section.

It may be provided, for example, that the flow labyrinth has first and second projections, which are opposite to one another and disposed offset in relation to one another in the direction of flow and the spacing between which is variable. The inflowing casting material undergoes a deflection in each case at the first and second projections, a considerable momentum being transferred to the first and/or second projections, so that the projections change their relative position and, as a result, reduce the flow cross-section of the flow labyrinth.

The first projections preferably are adapted to be offset in relation to the second projections in the direction of flow. The first projections are consequently movably held, whereas the second projections are fixedly formed. If the inflowing casting material impinges on the first projections, as a result the latter change their position in relation to the second projections and thereby reduce the flow cross-section of the flow labyrinth.

In the case of a configuration of the venting unit according to the invention that is structurally particularly simple, the first projections are held on a movable mounting. The mounting may, for example, take the form of a displaceable slide, which is movable back and forth between a first end position, in which the flow labyrinth has a relatively large flow cross-section, and a second end position, in which the flow labyrinth has a comparatively small flow cross-section. The slide is preferably held on a linear guide, which may be formed, for example, as a dovetail guide.

As already explained, it is advantageous if the first projections are adapted to be offset by liquid casting material flowing into the flow labyrinth. It may be provided, for example, that the first projections can be displaced by the liquid casting material, the flow cross-section of the flow labyrinth being reduced as a result.

It is of advantage if the first projections are adapted to be offset counter to an elastic restoring force. As a result, the first projections can be transferred from a rest position, which they assume as long as they are not impinged by liquid casting material, into a working position, in which the flow labyrinth has a flow cross-section that is reduced in comparison with the rest position. The transfer from the rest position into the working position takes place counter to the action of the elastic restoring force. If the first projections are no longer impinged by the casting material, they automatically resume their rest position on account of the restoring force acting on them.

It is particularly advantageous if the first projections are adapted to be arrested in their working position. It has been found that this makes it easier to remove the solidified casting material from the flow labyrinth, since the arresting of the first projections means that the solidified casting material is not subjected to any force by the elastically prestressed first projections.

Liquid casting material is usually injected into the mold cavity by means of an injection piston, then fills the mold cavity as completely as possible and then flows at very high speed to the inlet of the flow labyrinth. To avoid the movable first projections being damaged by the casting material flowing into the flow labyrinth at high speed, it is of advantage if the liquid casting material first impinges on a fixed projection and only then on a movable projection, undergoing a deflection at each of the projections. Inflowing casting material consequently first impinges on a fixed projection, at which it is deflected and thereby transfers a considerable momentum to the fixed projection. As it flows further into the flow labyrinth, the liquid casting material then impinges at already reduced speed on a movable projection, at which it undergoes renewed deflection, this movable projection at the same time being offset in relation to the fixed projection while thereby reducing the flow cross-section of the flow labyrinth. The then clearly slowed liquid casting material may subsequently impinge on a further fixed projection, at which it is once again deflected to impinge again subsequently on a movable projection. This process may be repeated a number of times, the respective deflection of the casting material at a movable projection leading to an additional movement of the movable projections on account of the transfer of momentum occurring, and consequently leading to a further reduction in the flow cross-section of the flow labyrinth.

Within the flow labyrinth, the entering casting material cools down greatly and finally solidifies. It is therefore of advantage if the flow labyrinth is formed by a material that conducts heat as much as possible, since particularly effective heat removal can be ensured as a result.

In the case of a particularly preferred configuration of the venting unit according to the invention, it comprises a venting block with a first and a second block part, the first block part being fixable on a first die half of the die casting device and the second block part being fixable on a second die half of the die casting device, and the two block parts forming between them a flow channel, into which first projections, disposed on the first block part, and second projections, disposed on the second block part, protrude to form a flow labyrinth, the first projections and/or the second projections being movably held respectively on the first and second block part. The mold cavity of the die casting device is usually formed by two die halves, the first die half being movably held and the second die half being fixedly held, so that, after completion of the casting operation, the casting produced can be easily removed from the mold cavity by the first die half being moved away from the second die half. The venting unit forms a venting block with two block parts. In this case, the first block part may be disposed on the movable die half and the second block part may be disposed on the fixed die half, so that, by opening the mold cavity, the flow labyrinth disposed between the two block parts can also be opened. The flow labyrinth is formed by the projections disposed on the respective block part, and to change the flow cross-section of the flow labyrinth the first and/or second projections are movably held on the respective block part.

In the case of an advantageous embodiment of the invention, the first and/or second projections are fixed on a holding plate movably mounted respectively on or in the first or second block part. The holding plate may take the form of a slide which is, for example, displaceably mounted on or in the respective block part by means of a linear guide.

It is advantageous if the holding plate is displaceable counter to the action of an elastic restoring force. A first end position is automatically assumed by the holding plate on account of the elastic restoring force acting on it as long as liquid casting material still does not enter the flow labyrinth. When liquid casting material enters, the holding plate can be displaced out of the first end position while thereby reducing the flow cross-section of the flow labyrinth.

At least one end position of the holding plate is preferably adjustable. An adjusting element, for example an adjusting screw, may be used for this purpose, forming a stop for the holding plate against which the holding plate is pressed on account of the elastic restoring force acting on it as long as casting material still does not enter the flow labyrinth.

It is advantageous if the position of the first and/or second projections can be sensed by means of a measuring sensor. This makes improved monitoring and documentation of the casting operation possible by allowing a measuring record to be prepared in each case for the castings produced and from which the position of the first and/or second projections during the production of the casting can be taken.

An electrical signal transmitter may be used, for example, as the measuring sensor, in particular it may be provided that the position of the first and/or second projections can be sensed by means of a position encoder. The signal transmitter may be connected to a control unit of the die casting device by way of a signal line.

The holding plate on which the first or second projections are held is advantageously arrestable. This makes it easier to open the flow labyrinth to remove casting material solidified in it.

As explained at the beginning, the invention relates not only to a venting unit of the type stated above but also to a die casting device with a venting unit of this kind. The die casting device comprises a mold cavity that is adapted to be filled with liquid casting material and a gas suction device that is connected to the mold cavity, the venting unit being connected between the mold cavity and the gas suction device. The mold cavity may be connected to the inlet of the flow labyrinth of the venting unit by way of a venting channel of the die casting device, and the outlet of the flow labyrinth may be connected to the gas suction device by way of a suction line. It is advantageous in this case if a suction valve is connected in the suction line.

The following description of a preferred embodiment of the invention serves for more detailed explanation in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic representation of a die casting device according to the invention with a venting unit according to the invention;

FIG. 2 shows an enlarged representation of the venting unit from FIG. 1 with movable projections in a first end position and

FIG. 3 shows an enlarged representation of the venting unit from FIG. 1 with movable projections in a second end position.

DETAILED DESCRIPTION OF THE INVENTION

Schematically represented in FIG. 1 is a die casting device 10 according to the invention, which has a first, movable die half 11 and a second, fixed die half 12, which interact in the customary way with a die closing unit that is known per se, and therefore not represented in the drawing. Said closing unit comprises a movable platen and a fixed platen, which are not represented in the drawing to achieve a better overview and on each of which one of the two die halves 11, 12 is held in a known way. By means of the die closing unit, a predeterminable closing force can be exerted on the two die halves 11, 12. The two die halves 11, 12 form between them a mold cavity 14, which has the form of a casting to be cast and into which a casting material, for example a molten metal, preferably liquid aluminum or magnesium material, can be injected. For this purpose, the mold cavity 14 has an inlet opening, which is usually referred to as the “gate” and in FIG. 1 is provided with the designation 15. By way of an inlet channel 17, the gate 15 is in connection with a casting chamber 18, which has a filling opening 19 and in which an injection piston 21 is displaceably mounted.

The injection piston 21 is held on a piston rod 22, which is fixed by its end that is remote from the injection piston 21 on a working piston 24. The working piston 24 is displaceably mounted in a working cylinder 26 of a drive unit provided overall with the designation 27. The drive unit 27 has a pressure cylinder 29, which is hydraulically coupled to the working cylinder 26 and in which a pressure piston 30 is displaceably mounted. On its end face that is toward the working cylinder 26, the pressure piston 30 has a thrust pin 31, which enters the working cylinder 26 on the side of the working cylinder 26 that is remote from the piston rod 22.

The pressure cylinder 29 is in flow connection by way of a pressure line 33 with a pressure accumulator which is known per se, and therefore not represented in the drawing, and which receives pressurized hydraulic fluid. An electrically controllable control valve 34 in the form of a solenoid is connected into the pressure line 33 and can be used for opening and closing the flow connection between the pressure accumulator (not represented in the drawing) and the pressure cylinder 29 in a defined manner.

The working cylinder 26 is in flow connection by way of an outlet line 36 with a storage tank 37 for hydraulic fluid, so that hydraulic fluid can be delivered from the working cylinder 26 to the storage tank 37 by way of the outlet line 36.

Approximately midway along it in the longitudinal direction, the piston rod 22 carries a bush 39, fixed on which is a carrying arm 40, which at the end carries a measuring rule 41, which interacts with a position encoder 42.

The position encoder 42 is in connection by way of a signal line 44 with an electrical control unit 46, to which the control valve 34 is also connected by way of a control line 48.

The die casting device 10 has a gas suction device 50, which is known per se, and therefore only schematically represented in the drawing, and which is in flow connection with the mold cavity 14 by way of a venting channel 52 extending from the mold cavity 14, a venting unit 55 adjoining the venting channel 52 and a suction line 57 adjoining said venting unit. An outlet valve 59, which is configured as a solenoid and is connected to the control unit 46 by way of a control line 60, is connected into the suction line 57.

The venting unit 55 is shown enlarged in FIGS. 2 and 3. It forms a venting block 62 with a first block part 63, which is fixed on the movable die half 11, and with a second block part 64, which is fixed on the fixed die half 12. The two block parts 63 and 64 form between them a flow channel 66, which adjoins the venting channel 52 and is connected to the suction line 57 by way of an outlet channel 67 passing through the second block part 64. Protruding into the flow channel 66 are rib-shaped first projections 69 and likewise rib-shaped second projections 70, which are opposite to one another and disposed offset in relation to one another in the direction of flow, engaging in one another in a comb-like manner and forming between them a flow labyrinth 72.

The first projections 69 are fixed by means of a screw connection that is known per se, and therefore not represented in the drawing to achieve a better overview, on a holding plate 74, which is formed in the manner of a slide and is mounted displaceably in a recess 77 of the first block part 63 with the aid of a linear guide 75, for example a dovetail guide. By way of a thrust rod 79, the holding plate 74 is acted upon by a compression spring 80 with an elastic restoring force. The compression spring 80 is disposed in a spring housing 82, which is fixed on the outside of the first block part 63, on the side remote from the movable die half 11, and is passed through by the thrust rod 79, which at its free end carries an extension arm 83, which interacts with an electrical position encoder 85 and in the first end position of the holding plate 74, represented in FIG. 2, lies against a switching contact 86. The position encoder 85 and the switching contact 86 are connected to the control unit 46 by way of respective signal lines 87 and 88, which are only shown in part in the drawing to achieve a better overview.

Disposed between the spring housing 82 and the extension arm 83 is an arresting mechanism 90, which is passed through by the thrust rod 79. The arresting mechanism 90 has in a way known per se, and therefore not represented in the drawing, arresting means, for example tensioning means, with which the thrust rod 79, and thereby also the holding plate 74 and the first projections 79, can be arrested in any position desired.

The holding plate 74 is acted upon by the compression spring 80 with a spring force in the direction of the movable die half 11. In the position represented in FIG. 2, the holding plate 74 lies with an end face 92 remote from the thrust rod 79 against an adjustable stop in the form of an adjusting screw 93, which predetermines the position of the holding plate 74, and consequently also the position of the first projections 69.

A temperature measuring sensor 95, which is connected to the control unit 46 by way of a signal line 96, enters the first block part 63.

The second projections 70 are immovably fixed on the second block part 64, it likewise being possible for a screw connection that is known per se, and therefore not represented in the drawing, to be used to fix them.

The holding plate 74, and consequently also the first projections 69, are displaceable back and forth between the first end position, represented in FIG. 2, in which the holding plate 74 lies with its end face 92 against the adjusting screw 93, and the second end position, represented in FIG. 3, in which the end face 92 assumes a distance from the adjusting screw 93. In the first end position, the first projections 69 assume a relatively great distance from the second projections 70, so that the flow labyrinth 72 has a relatively large flow cross-section. With increasing displacement of the holding plate 74 into its second end position, the flow cross-section of the flow labyrinth 72 is reduced. This is particularly clear from FIG. 3.

To produce a casting, a molten metal is injected into the mold cavity 14 by means of the injection piston 21. At the beginning of the casting operation, the injection piston 21 assumes a withdrawn position, in which it exposes the filling opening 19, so that the molten metal can be filled into the casting chamber 18. Subsequently, the injection piston 21 is pushed into the casting chamber 18 by means of the drive unit 27. The path covered by the injection piston 21 can be sensed by means of the position encoder 42. At first, the liquid casting material is transported up to the gate 15 by means of the injection piston 21 and at the same time air and casting gases are extracted from the mold cavity 14 by means of the gas suction device 50 by way of the venting channel 52, the flow labyrinth 72, the outlet channel 67 and the suction line 57, with the outlet valve 59 being open.

Once, according to the signal of the position encoder 42, the injection piston 21 has reached a position in which the molten metal has reached the gate 15, the drive unit 27 is activated by the control unit 46 by way of the control valve 34 in such a way that the injection piston 21 is pushed at high speed further into the casting chamber 18 within a very short time and the previously evacuated mold cavity 14 is completely filled with liquid casting material. The liquid casting material 100 finally reaches the inlet 98 of the flow labyrinth 72 and is first deflected by a second projection 70, to subsequently impinge on a first projection 69. This is represented in FIG. 2. The liquid casting material 100 thereby impinges at very high speed on a first projection 69, to which a considerable momentum is transferred as a result. This has the consequence that the first projection 69 is displaced together with the holding plate 74 counter to the action of the compression spring 80 in the direction away from the adjusting screw 93, so that the initially considerable flow cross-section of the flow labyrinth 72 by way of which gas is extracted from the mold cavity 14 is reduced. The successive deflections that the liquid casting material 100 undergoes within the flow labyrinth 72 have the effect of slowing the casting material 100. At the same time, heat is dissipated from the liquid casting material 100 to the block parts 63 and 64 as well as to the projections 69 and 70 and to the holding plate 74, so that the temperature of the casting material 100 is greatly reduced and it finally solidifies within the flow labyrinth 72, still before the casting material 100 reaches the outlet 99 of the flow labyrinth 72.

The casting material 100 hardening in the mold cavity 14 can be subjected to a very high pressure by the injection piston 21 for the secondary compression of the casting material 100.

Once the casting operation has taken place, the mold cavity 14 can be opened by displacing the movable die half 11, the flow labyrinth 72 also being opened at the same time, since the first block part 63, fixed on the movable die half 11, is brought along with the movable die half 11 to a distance from the second block part 64. The casting material 100 that has hardened within the flow labyrinth 72 can consequently be easily removed from the flow labyrinth 72. To make the removal easier, the holding plate 74 can be arrested together with the first projections 69 in their second end position, represented in FIG. 2, by means of the arresting mechanism 90, so that the casting material 100 that has hardened in the flow labyrinth 72 is not subjected to any force by the first projections 79.

After removal of the solidified casting material 100 from the flow labyrinth 72 and removal of the casting from the mold cavity 14, the first block part 63 together with the movable die half 11 can be moved again in the direction of the second block part 64, or in the direction of the fixed die half 12, so that a renewed casting operation can subsequently be carried out.

The movable mounting of the first projections 69 allows the flow labyrinth 72 to have a considerable flow cross-section at the beginning of a casting operation, so that the mold cavity 14 can be reliably evacuated by the gas suction device 50. However, to avoid liquid casting material 100 being able to flow through the flow labyrinth 72 during the casting operation, the flow cross-section thereof can be reduced on account of the movable mounting of the first projections 69, the first projections 69 being displaced by the casting material 100 that enters the flow labyrinth 72. This dispenses with the need for electrical, hydraulic or pneumatic control of the movement of the first projections 69. 

1. Venting unit for a die casting device which has a mold cavity that is adapted to be filled with liquid casting material and a gas suction device that is connected to the mold cavity for extracting gas from the mold cavity by suction, the venting unit comprising a flow labyrinth, the inlet of which is adapted to be connected to the mold cavity and the outlet of which is adapted to be connected to the gas suction device, and the flow cross-section of the flow labyrinth being variable.
 2. Venting unit according to claim 1, wherein the flow cross-section of the flow labyrinth is adapted to be varied by liquid casting material flowing into the flow labyrinth.
 3. Venting unit according to claim 1, wherein the flow labyrinth has first and second projections, which are opposite to one another and disposed offset in relation to one another in the direction of flow and the spacing between which is variable.
 4. Venting unit according to claim 3, wherein the first projections are adapted to be offset in relation to the second projections in the direction of flow.
 5. Venting unit according to claim 3, wherein the first projections are held on a movable mounting.
 6. Venting unit according to claim 3, wherein the first projections are adapted to be offset by liquid casting material flowing into the flow labyrinth.
 7. Venting unit according to claim 3, wherein the first projections are adapted to be offset counter to an elastic restoring force.
 8. Venting unit according to claim 3, wherein a first projection is disposed behind a second projection in the direction of flow of liquid casting material flowing into the flow labyrinth.
 9. Venting unit according to claim 1, wherein the venting unit comprises a venting block with a first and a second block part, the first block part being fixable on a first die half of the die casting device and the second block part being fixable on a second die half of the die casting device, and the two block parts forming between them a flow channel, into which first projections, disposed on the first block part, and second projections, disposed on the second block part, protrude, the first projections and/or the second projections being movably held respectively on the first and second block part.
 10. Venting unit according to claim 9, wherein the first and/or second projections are fixed on a holding plate movably mounted respectively on or in the first or second block part.
 11. Venting unit according to claim 10, wherein the holding plate is displaceable counter to the action of an elastic restoring force.
 12. Venting unit according to claim 10, wherein at least one end position of the holding plate is adjustable.
 13. Venting unit according to claim 9, wherein the position of the first and/or second projections can be sensed by means of a measuring sensor.
 14. Venting unit according to claim 10, wherein the holding plate is arrestable.
 15. Die casting device with a mold cavity that is adapted to be filled with liquid casting material and a gas suction device that is connected to the mold cavity for extracting gas from the mold cavity by suction and with a venting unit according to claim 1, which is connected between the mold cavity and the gas suction device. 